The measure, officially called the “Farmer Assurance Provision,” but dubbed the “Monsanto Protection Act” by opponents, would allow farmers growing GE or genetically modified crops, the most common of which are sold by agribusiness giant Monsanto, to sell their harvests even if the GMOs are being challenged in court.

Earlier this year, Blunt said he was disappointed that a similar provision was initially left out of the Fiscal Year 2013 Agricultural Appropriations bill.

“Lawsuits challenging things like the ‘environmental review’ undertaken by USDA have resulted in challenges to already planted and approved crops, such as alfalfa and sugar beets,” Blunt said when he introduced the bill. “As the economy continues to struggle, we must make sure that farmers have certainty that their planting decisions will not be upended by judicial intervention.”

Several corn and soybean growers’ associations have also endorsed the measure.

Food safety advocates say that Monsanto worked with legislators, including Blunt and Rep. Jack Kingston, R-Ga., to add the language to a continuing resolution, a spending bill that will avert a government shutdown for the remainder of the fiscal year.

Barbara Mikulski, D-Md., chairwoman of the Senate Appropriations Committee, of which Blunt is also a member, was criticized for allowing the rider to sneak into the continuing resolution. Mikulski’s office apologized for the provision last week, and said Mikulski was not yet chairwoman when the language was drafted.

“Senator Mikulski has a strong food safety record,” Mikulski spokeswoman Rachel MacKnight said in a statement. “As Chairwoman of the Appropriations Committee, Senator Mikulski's first responsibility was to prevent a government shutdown. That meant she had to compromise on many of her own priorities to get a bill through the Senate that the House would pass.”

President Barack Obama signed the resolution into law last week, but food safety groups are working to ensure that the rider, which is set to expire with the rest of the resolution in six months, is not included in future resolutions or budgets.

“We’re absolutely organizing to make sure it’s not slipped into another continuing resolution or another budget bill," Murphy said. "We’ve put in over 100,000 phone calls to Congress and the White House in less than a ten-day period. We’re going to fight this tooth and nail."

St. Louis-based Monsanto is among the largest corporate contributors to Blunt. Blunt received more than $64,000 from Monsanto between 2011 and 2012, making the company his sixth-largest corporate financier.

MU also receives substantial donations from Monsanto. In 2009, a $2 million grant from Monsanto helped MU fund a $9 million building for the Life Science Business Incubator. In 2011, Monsanto provided students with a three-year, $100,000 grant to research plant sciences.